Digital down-conversion circuit suitable for filtering multi-tone modulation system

The invention provides a digital down-conversion circuit suitable for a filtering multi-tone (FMT) modulation system, and aims to providing the digital down-conversion circuit which does not extract operation results of low-pass filters, can reduce the operation frequencies of the filters and reduce hardware resources and power consumption of equipment and is suitable for an FMT system according to the characteristics of an FMT signal. The digital down-conversion circuit is implemented by the following technical scheme: the working frequencies of M parallel frequency mixers are the same as the AD (analogue and digital) sampling rate fs, and the working frequencies of the parallel low-pass filters are fs/M; the M parallel low-pass filters 102 comprise K registers connected in series to the output ends of serial/parallel converters in sequence; the K registers are provided with K filter coefficients and are connected with an accumulator through K multipliers 204; an AD sampling signal passes through the M parallel frequency mixers, and a signal subjected to frequency mixing is sent into the serial/parallel converters 201 and passes through the M parallel low-pass filters 102 to obtain M digital baseband signals; M is the number of subcarriers of the FMT system and a natural number, and K is the number of orders of the filters and a natural number and is larger than or equal to M.